benkert



July 25, 1944. M. BENKERT 2,354,190

WELDING APPARATUS Filed March 21, 1942 2 Sheets-Sheet 1 July 25, 1944-l.. M. BENKERT 2,354,190

WELDING APPARATUS Filed Maron 21, 1942 2 sheets-sheet 2 jid,

INVENTOR /auyzls M evferz.

B A MIMQM Patented July 25, 1944 WELDING APPARATUS Louis M. Benkert,Detroit, Mich., assigner to Progressive Welder Company, Detroit, Mich.,a oorporation of Michigan Application March 21, 1942, Serial No. 435,655

7 Claims.

The present invention relates to welding apparatus and in particular isdirected to the provision of welding electrodes embodyingthermoelectrically responsive elements. 'Ihe present structures areimprovements upon the structural arrangements disclosed and claimed inthe copending application of Chester F. Leathers, Serial No. 415,015,led October 15, 1941, and assigned to the Weltronic Corporation.

As is described in greater detail in the above copending application,the thermoelectric control of resistance welding operations is highlybeneficial because it enables the duration of ow of welding current orthe intensity of the welding current, or other characteristics of thewelding cycle to be controlled in accordance with the temperature of thework within, or in the region of, the weld nugget. Thus, for example, inmaking successive welds, the period of current flow for successive weldsmay be automatically varied in such relation that in each instance thewelding current is caused to flow long enough to enable the formation ofa nugget oi predetermined size. but is interrupted as soon as such sizeis attained. This automatic control eliminates a wide variety oivariables which have heretofore been inherent 'in welding cycles andwhich are caused, for example, by the variation in area of theelectrodes, which is caused by the mushrooming thereof, variations inthe supply voltage, variation in the surface characteristics, thicknessor number of pieces being welded, variations in inductance of thewelding circuit, which are caused in making welds which are distributedover relatively wide surfaces, and variations due to the shunting awayof current from the weld in progress through adjacent welds.

It will be understood that in resistance welding operations, such asspot and projection welding operations, the work is clamped betweenoppositely disposed electrodes. The welding current path extends fromone electrode through the workpieces and thence through the otherelectrode. The high resistance points of this circuit are the twojunctions between the respective electrodes and the work, and thejunction or junctions between the engaging surfaces of the workpiecesthemselves. By virtue of the fact that the boundaries of the former twojunctions are open to the air, and by virtue of the further fact thatthe electrodes are supplied with cooling means, the former two junctionsare maintained at a considerably lower temperature than the workpiecejunctions and are, consequently, of lower resistance. Consequently, theheat builds up most rapidly at the workpiece junctions, enabling theformation therebetween of the weld nugget. There is, however, a definitetemperature gradient between the temperature in the body of the nuggetand the temperature in the bodies of the electrodes and, neglectingshunting effects; a temperature measurement at any point along thisgradient adorais a measure of the temperature in the weld nugget. Inaccordance with the invention of the above copending application, theshunting effects may be eliminated by seeing to it that the point oftemperature measurement is centrally located relative to the workengaging face of the electrode, and that the point of temperaturemeasurement is not farther from the body of the nugget than a point ashort distance inwardly of the electrode body from the work engagingface thereof. Within these limits it 'will be understood that ameasurement of the temperature of the electrode engaging face of thework, or a measurement oi' the temperature oi the work engaging face ofthe electrode is satisfactory.

With the foregoing general considerations in view, the principal objectsof the present invention are to provide an electrode structure embodyingthermoelectric means arranged to afford a temperature measurement whichis proportional to the temperature within or in the region of the weldnugget; to provide such structures wherein, more particularly, thethermoelectric elements are so disposed as to rprovide a measurementwhich is not substantially affected by shunting effects; to provide,more particularly, an arrangement wherein the thermoelectrlc elementsaord a direct measure, in one instance, of the temperature at the workengaging face of the electrode, and in another instance, at theelectrode engaging face of the work; to provide such arrangementsembodying an electrode tip formed to receive one or more thermocouplewires, which are disposed in certain instances to electrically engagethe electrode tip at the work engaging face thereof, and in certainother cases. to electrically engage the work at the electrode engagingface thereof; to provide such arrangements wherein the wire or wires ofthe thermocouple are centrally located relative to the work engagingface of the electrode tip,' so that the temperature measurements are notsubstantially affected by shunting eiiects; and to provide sucharrangements which may readily and economically be manufactured andwhich are positive and reliable in operation.

With the above as well as other objects in view, which appear in thefollowing description and in the appended claims, preferred butillustrative embodiments of the invention are shown in the accompanyingdrawings, through the several views of which corresponding referencecharacters are used to designate corresponding parts and in which:

Figure l is a view in central longitudinal secmenne -a-s of Fig. tieneiFig. 49 lsf-a view fin'horiz'ontal-section taken .tion of-an ielectrode structure embodying the inventiom ,1

Fig. 2 is an end view of the structure shown in Fig. 1:

Fig. .-3 .is afragmentary enlargedizview ,of-that part off-- thestructureshown Fig.. 11, which is encircled;

Fig. 4 is a view in horizontal section, taken'falong the line L-- ofFig. 8;

Fig. 5 is a View corresponding generally tot:

l "Q .The' wire-3 2., which hasgari insulating sheath 245, is receivedin a slot Il `provided'i'n a tapered plug 38. The plug 3B in turn has adrive fit within a. tapered bore 40 formed in the tip I4.

In assembung the wire :2 with the plug sa,

Fig. 4, showing the relation-,of -the elements at a predetermined stageof the assembly operation;

employed in the construction of Figs. l through;

Fig. 7 is an end view of a modification of theaiongthelime 9 9 of Fig.a.

Itwill be appreciated from -a'complete understanding -of' the present'invention `that the improve'ments thereof maybe embodiedinf electrodeconstructions -of widely 'differing type's.intended for Widely.differing speciflm-weldingprocesses.v

The herein :described embodiments of the invention are. therefore, to'bev regarded" in 'an illustra- 'tive and notina limiting sense'.

I2 is complementary thereto. VIn the assembled positionsof the parts,the fiat faces of the mem..

bers vH1 and lI2 directly abut each other and these members are held .inassembled relation by means of a. collar I6, which engages ashoulder,consti tuted by a llink lion the body I2. The-collar I8 is provided withthreads which cooperate with *correspondingl threads Aon theholder I0,whereby" the collar I6 may b e tighteneddown so as to 'securelyvclampthe holder IIJ and the body I2 together. 'I'he members .I land I2 areheld against femme-rotation during ,this tightening opera-A tion bymeansl of one or more dowel pins 20.

The body l2 and, i1' desired, the holder I0 are cored out, as indicatedat,22 vto afford a passage through which' a coollngliquid may becirculated.

Thec'oolant is preferably.. introduced through a conduit, and thepassage 22 may. as will be understood, communicate with a suitableexhaust conduit (not shown). Any suitable coolant may be utilized,although, in 4accordance with the inven`tlon""disclosed` and claimed inthe copending an' insulated length of the wire may be relatively looselywrapped in-one or more folds of a strip 42 ofconducting material, forexample, copper Fig. 8 is a view in elevation of the plug elementstr-ip, sutllcient lthicknesses of the strip 42 being used so that `the.assembly comprising the wire 'and the strip may be relatively readilyinserted into the slot 36 in the plug 38. Thereafter, the plug 38 isdriven into the bore 40, duringwhich `driving the plug 38 isconstricted, thereby constricting the slot 36 and causing the stripv 42to very tightly wedge the wire 32. By properly proportioning theoriginal taperv of the plug 38 relative to the taper of the bore 4D, itis possible to cause this tight wedgin'g relation to extendsubstantially throughout' the*v full depth of the slot 3B. On the'otherhand, although an exceedingly tight Wedging action is attained, themultiple plies ofthe strip 42 serve to protect the insulation 34 aroundthe wire 32.

The plug 38 is preferably dimensioned so that when it is driven to thefull depth of the bore 40, the larger end thereof projects outwardlyfrom the face v3l! to some extent, and at the conclusion of the drivingoperation, this excess metal is ground away or otherwise removed,thereby affording a ilush relation between the surface 30 and the outerend of the plug 2i.

' develop sufficient heat at the work engaging face application ofLeathers and Moehlenpah, Serial No. 415,184, nieu october 1c, 1941,1t ispreferred to use brine atv a' temperature well below the freezing pointof'water.

"The `replaceable tip I4'is provided witha fiat inner-*face 25, whichseats against the corre' sponding flat outer face of thefbody I2, andthe"members I4 Vand I2 are heldin assembled relapotent-fari; obtained. formeasuring nurposes, byl

utilizingthelectrode'as one element vofl a thermocouple `and byembedding'therein a conducting wire 32. 'which with vthe electrode formsa thermocouplel For example, assuming the e1ecof the electrode to burnaway the insulation 34 throughout a distance of a few thousandths of aninch from the end of the wire 32, leaving this extreme end portion ofthewire I2 in a bare condition. v4The pressure of the work against theelectrode face bends this exposed end of the wire over into solidengaging relation to the immediateiy adjacent strip 42, which strip 42in tum is in solid engaging relation to the plug Il.v The thermoelectricpotential is thus developed at the junction between the wire 32 and thestrip 42, which junction, as lust mentioned, is at or im mediatelyadjacent the work engaging face of the electrode.

The slot 36 in the plug 38 opens at its inner end into an enlarged bore64, which in the assembled position of the parts registers with a bore46 in the tip I4. The bore 4I ln turn opens into 'a shallow counterbore48, which receives an insulating disk 50 and a conducting contact memberV52, to 'which the end of the wire 32 is soldered or otherwiseelectrically and mechanically connected.

The counterbore 48 registers with a corresponding counterbore 5I in thebody I2, which receives an insulating disk 53 and a cooperatingspring-like contact member $4. The spring-like contact member 54 isconnected to a cooperating wire 5B, which extends through connectingradial and longitudinal passages Il and III to a jack 62. The externalconnection to the wire 56 is made through a plug 64, which istelescopingly received in the jack 62. The other external connection forthe thermocouple may be applied directly to the electrode body, as willbe understood.

When the tip |4 is seated upon the body I2, the contact member 52engages and slightly depresses the spring-like contact member 54,thereby completing an efficient electrical connection between the wires32 and 56, and a similar electrical connection between the wire 56 andthe external circuit is made through the plug and jack assemblycomprising the members 62 and 64.

It will be understood that as the face of the electrode wears away, oris ground away in dressing operations? the end of the plug 38 iscorrespondingly ground away. Similarly, the strip l2 and the end of thewire 32 are ground away. After each dressing, the initial weldingoperations burny away an additional short length of the insulation 34and again cause the bared end of the wire 32 to solidly engage the stripI2, thereby again completing the thermocouple at a point immediatelyadjacent the new face of the electrode. Following each dressingoperation, accordingly, the thermocouple is automatically renewed.

In the modified embodiment of the invention shown in Figs. 7, 8 and 9,two thermocouple wires and |02 are embedded in the electrode tip |00,and the laminated or folded material |06 is formed of insulatingmaterial such as mica. With this construction, accordingly, the exposedends of the wires |00 and |02, which in the original manufacture and insubsequent dressing operations are continuously ground flush with thework engaging face |04a o'f the electrode, directly engage the surfaceof the work and two thermal E. M. F.s are produced, each of which'isdirectly determined by the temperature of the surface of the work. Oneof these thermal E. M. F.s is developed at the junction between the wire|00 and the work, and the other is developed at the junction between thewire |02 and the work. The thermal E. M. F. developed across the twowires |00. and |02 is consequently the algebraic sum of thejust-mentioned two E., M. F.s.

By proper selection of the material from which the wires |00 and |02 areformed, with reference to the work being welded, accordingly, it ispossible to have the just mentioned two thermal E. M. F.s actcumulatively. Thus, assuming the wire |00 is formed of copper and thework being welded is aluminum, the copper is thermally positive withrespect to the aluminum. Assuming, further, that the ywire |02 is formedof constanwith longitudinal bores ||4 and H6. As before, also, the endsof the wires |00 and |02 are connected to plug elements ||8 and |20,which respectively receive jacks |22 and |24, to which the externalconnections may be made in any suitable manner.

As in the previous embodiment, it is preferred to position the wires |00and |02 relatively near the center of the electrode face, so as tominimize or eliminate the previously described shunting effects.

By way of review, it will be appreciated from the foregoing that both ofthe herein described embodiments may generically be characterized asaffording a temperature measurement which enables control of the weldingoperation in accordance with the temperature in the region of the weld.In a more restricted sense, both embodiments aord a measurement which issubstantially unaffected by shunting effects. Further, in theembodimentfof Figs. 1 through 6, the actual temperature measured is thetemperature at the work engaging face of the electrode, Whereas in theembodiment of Figs. 'l through 9, the actual temperature which ismeasured is the temperature at the electrode engaging face of the workAlthough only two specic embodiments of the invention have beendescribed in detail, it will be appreciated that further modications inthe form, number and arrangement of parts may be made without departingfrom the spirit and scope of the invention.

What is claimed is:

1. An electrode having a work engaging face provided with a bore whichopens through said face, an insulated wire received in said bore, and acontractable holding member received in said bore, said member being sodimensioned relative to said bore that when it is introduced therein itis contracted by said bore, said contraction serving to enable saidmember to wedgingly hold said wire in said bore with an end of said wireexposed upon said face, pressure exerted between said face tan, thealuminum work is thermally positive with respect to the constanten, andthe E. M. F. between the wires 00 and |02 is thus the arithmetic sum ofthe copper to aluminum E. M. F. and the aluminum to constantan E. M. F.

As in the previous embodiment, the wires |00 and |02 are initiallywrapped in the insulation |03, which is thereafter initially compressedand snugly introduced into the slot formed in the plug |03. Thereafter,the plug |08 is driven into the bore in the electrode tip |04, therebyrestricting the slot and securely embedding the wires |00 and 02 inplace. and in such relation that they are insulloated from each otherand from the electrode tip 1 In the embodiment now being described,separate bores ||0 and ||2 are provided for the wires |00 and |02,respectively, which bores extend radially, as appears in Fig. 7, andcommunicate and the work serving to conductively couple the said end ofthe wire to associated means which, with said wire, forms athermocouple.

2. The structure of claim 1, wherein said associated means comprises thesaid member.

3. The structure of claim 1, wherein said associated means comprises asecond wire received in said member and wedgingly held in place thereinby said contraction with an end of said wire exposed upon said face.

4. The structure of claim 1, wherein said associated means comprises thesaid member and the body of the electrode.

5. The structure of claim 1, wherein said associated means comprises asecond wire received in said member and wedgingly held in place thereinby said contraction with an end oi said wire exposed upon said i'ace,the exposed ends of said wires being electrically coupled together bysaid pressure.

6. The structure of claim 1, wherein said assoelated means comprises asecond wire received in said member and wedgingly held in place thereinby said contraction with an end of said wire exposed upon said face, theexposed ends of said wires being electrically coupled together throughthe work by said pressure.

7. The structure of claim 1 wherein said associated means comprises thebody oi' the electrode.

LOUIS M. BENKERT.

